1. Field of the Invention
This invention relates to heat exchangers which are used in air conditioning and refrigeration industry and are adapted to transfer heat energy between a fluid flowing through the heat exchanger and a gas in contact with the external surface of the heat exchanger. More particularly the invention relates to a method of manufacture of multiple circuit heat exchanger coils which can be utilized alternately as an evaporator or as a condenser in heat pump systems.
2. Description of the Prior Art
Heat pump systems normally comprise an indoor heat exchanger or coil which acts as an evaporator during operation of the systems for cooling purposes, and an outdoor heat exchanger or coil which, at the same time, acts as a condenser.
Some applications of air conditioning or heat pump systems require a large heat exchanger capacity. To provide sufficient and effective cooling or heating of the large interior spaces of buildings it is required to utilize large amounts of refrigerant flowing through the heat exchangers to enhance the heat transfer characteristics. This requires a greater heat exchanger surface which normally is attained by long lengths of tubing, or a larger size tubing.
A plurality of helical tubes of smaller diameter, wound in series, with sufficient amount of surface and pressure drop to assure that the refrigerant is evaporated or condensed have been used. This approach requires inlets and outlets for the refrigerant mounted in the middle of the coil. This type of arrangement is expensive and difficult in assemblying the coils in the casing of the heat exchanger.
Utilization of a plurality of helical coils wound in parallel and interwoven in the same directions provides efficient heat transfer along the whole path of refrigerant through the coils and allows to reduce the length of casing of the heat exchanger particularly where the use of less space is important. Double or multiple coils include a double or multiple lead at each end of the heat exchange element. In making the heat exchange element of the foregoing type two or more tubes are wrapped around the forming drum in parallel contiguous position. After removing the forming drum the ends of the tubes forming the leads of the coils have been cut off to provide the element of desired length. By merely cutting the ends of the tubes off a large gap between the ends and the wound turns of the tubes will result if both leads are terminated at the same point. This gap increases the length of the heat exchange element which is not desirable in the installations where the space is an important factor.